<template>
    <el-scrollbar ref="scrollContainer" :vertical="false" class="scroll-container" @wheel.native.prevent="handleScroll">
      <slot />
    </el-scrollbar>
  </template>
  
  <script>
  const tagAndTagSpacing = 4 // tagAndTagSpacing
  
  export default {
    name: 'ScrollPane',
    data() {
      return {
        left: 0
      }
    },
    computed: {
      scrollWrapper() {
        return this.$refs.scrollContainer.$refs.wrap
      }
    },
    methods: {
      handleScroll(e) {
        const eventDelta = e.wheelDelta || -e.deltaY * 40
        const $scrollWrapper = this.scrollWrapper
        $scrollWrapper.scrollLeft = $scrollWrapper.scrollLeft + eventDelta / 4
      },
      moveToTarget(currentTag,tagList) {
  
        const $container = this.$refs.scrollContainer.$el
        const $containerWidth = $container.offsetWidth
        const $scrollWrapper = this.scrollWrapper
        // const tagList = this.$parent.$refs.tag
  
        let firstTag = null
        let lastTag = null
  
        // find first tag and last tag
        if (tagList.length > 0) {
          firstTag = tagList[0]
          lastTag = tagList[tagList.length - 1]
        }
  
        if (firstTag === currentTag) {
          $scrollWrapper.scrollLeft = 0
        } else if (lastTag === currentTag) {
          $scrollWrapper.scrollLeft = $scrollWrapper.scrollWidth - $containerWidth
        } else {
          // find preTag and nextTag
          const currentIndex = tagList.findIndex(item => item === currentTag)
          const prevTag = tagList[currentIndex - 1]
          const nextTag = tagList[currentIndex + 1]
  
          // the tag's offsetLeft after of nextTag
          const afterNextTagOffsetLeft = nextTag.$el.offsetLeft + nextTag.$el.offsetWidth + tagAndTagSpacing
  
          // the tag's offsetLeft before of prevTag
          const beforePrevTagOffsetLeft = prevTag.$el.offsetLeft - tagAndTagSpacing
  
          if (afterNextTagOffsetLeft > $scrollWrapper.scrollLeft + $containerWidth) {
            $scrollWrapper.scrollLeft = afterNextTagOffsetLeft - $containerWidth
          } else if (beforePrevTagOffsetLeft < $scrollWrapper.scrollLeft) {
            $scrollWrapper.scrollLeft = beforePrevTagOffsetLeft
          }
        }
      }
    }
  }
  </script>
  
  <style >
    .scroll-container {
      white-space: nowrap;
      position: relative !important;
      overflow: hidden !important;
      width: 100%;
    }
    .scroll-container  .el-scrollbar__bar {
      bottom: 0px;
    }
    .scroll-container  .el-scrollbar__wrap {
      height: 49px;
    }
  </style>
  